FPrint

PPA description

FINGERPRINT AUTHENTICATION FOR UBUNTU BASED ON FPRINTD
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This PPA contains packages that add a comprehensive fingerprint-based authentication functionality to Ubuntu, including a seamless integration into GNOME 2.x, Unity and GNOME 3.x. Supported releases of Ubuntu are 12.04, 14.04, 16.04 and 16.10. Please note that since version 12.10 these packages are present in the standard repositories (still, this PPA supports a wider range of fingerprint readers).

(Note: If you have experimented with fingerprint authentication before and have changed your /etc/pam.d/common-auth, you may be presented with a screen asking whether you want to override those changes. Select Yes. Under very special circumstances, you may get an error saying
pam-auth-update: Local modifications to /etc/pam.d/common-*, not updating.
pam-auth-update: Run pam-auth-update --force to override.
In this case, run “sudo pam-auth-update --force”, exactly as suggested, and enable the fprintd profile manually. Leave the standard system profiles (Unix, Keyring and ConsoleKit) enabled as well.)

3. Launch “fprint project demo” and check that you can enroll and verify your fingerprints and that your reader is indeed supported.
4. Run “fprintd-enroll” in terminal to save your fingerprint.

Known (minor) issues
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1. No fingerprint and password at the same time
At the moment, you cannot type in your password right away when you are asked for fingerprint. You need to make the fingerprint authentication fail first (swipe wrong finger or let it time out) before you are asked for password. This is a limitation of PAM because its modules mustn't be threaded and hence cannot support multiple means of authentication at the same time. (The old ThinkFinger used to do this, but it was a gross hack which caused many troubles.) A possible solution to this limitation is to make gdm, screensaver and policykit-1 support multiple alternative PAM stacks. Fedora 12 has enhanced the GDM login screen with a button that switches between password and fingerprint authentication mode (screenshot: http://bit.ly/cEjYbo). Similar enhancements for screensaver and PolicyKit are being worked on by Red Hat (see https://bugzilla.redhat.com/show_bug.cgi?id=500338).

Note on keyrings and passwordless logins
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If you log in with your fingerprint, the default keyring manager will not have access to your password or any other secret data to decrypt your enciphered content with. The same applies to encrypted partitions and their automatic unlocking with libpam-mount or eCryptFS. Please note that it is not possible to unlock the keyring unless you have typed in your password (there's nothing to unlock it with, and having a key stored somewhere on disk is a very naïve and insecure solution). If you are wondering why fingerprint authentication cannot provide any secret data to replace the standard password mechanism, please read section “How fingerprint authentication works” below.

There are basically 2 possible solutions to the keyring issue:
1. Keep logging in with your password as before (you will need to make the fingerprint authentication fail first by scanning a wrong finger) and then use fingerprint only for sudo and locked screens. This way you will have your standard password available in your session, and keyring and encrypted partitions will work as before.
2. Remove the password from your default keyring. This way the passwords in it will be stored unencrypted, but this may be perfectly acceptable for you if you store only insensitive data in it (such as passwords to Wi-Fi networks). If you decide to take this route, here is a short how-to: Go to Applications > Accessories > Passwords and Encryption Keys, card Passwords, right click on Passwords: login, Change Password and set it to empty string.

Note on gksu (not an issue in default install since 11.10)
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When you run Synaptic or a similar graphical application that requires unlimited, full root privileges, the standard authentication window doesn't get displayed. Yet the fingerprint reader is ready, and a swipe will authenticate the user. The informative window not appearing is a major bug in GNOME's gksu, which will never be fixed because of its inner limitations. Instead, a replacement called gksu-polkit is being developed (its latest version is in this PPA). With this package installed, you can then adjust your menu items to call gksu-polkit instead of gksu. Go to System > Preferences > Main Menu, select the item you want to modify, click Properties and in the Command field change "gksu [options...] command" to "gksu-polkit /full/path/to/command" (note that you need to drop all the options to gksu, if any, and full path to command is required).
Note that nowadays all graphical applications should run with standard user's privileges, not root's. When they need to perform any administrative action, they should get root privileges for this single action (and not for the whole process) via PolicyKit, the new privilege management framework. This is what applications such as “Users and Groups” or “Time and Date” do. Applications that still rely on gksu are outmoded and should be ported to the new framework.
Offending applications include: Synaptic (bug #227482, not a default app since Oneiric, fixed since Precise), Software Sources (fixed in Oneiric), Computer Janitor (fixed in Maverick), Update Manager (fixed in Maverick), or gdebi, the deb installer (bug #189617, not a default app since Maverick)
Gksu-polkit was written as a temporary solution for the applications that still rely on the old (and now deprecated) gksu.

How fingerprint authentication works
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When you set up fprintd and enroll your fingerprint for the first time, the scan (basically just an image) gets saved on your hard drive (it goes into /var/lib/fprint/<username>). Then when you try to authenticate yourself, the system gets another scan from reader, and it checks whether the picture received looks more or less the same as the picture stored on disk. If that is the case, the user is let in.
This implies that the fingerprint authentication cannot serve as a source of any secret data that could then be used as a password (to decrypt the content of the default keyring or to unlock encrypted partitions, for instance).
Theoretically, one could think of a mathematical reduction of the fingerprint to a number, a reduction that would be comprehensive as well as consistent so that different scans of the same finger always be reduced to the same number but scans of different fingers produce different numbers. Then only a hash of such a description of the fingerprint pattern could be saved on disk for the sake of authentication, and the number itself could be used as a secret, not a particularly strong secret since you keep it publicly at a well known place (your fingertip) and keep leaving copies of it on everything you touch, but at least it wouldn't be stored on your disk, and it could be used for decrypting the keyring, for instance.
However, such a technology is not available at the moment, and it doesn't seem to be feasible either. One hundred years of forensic dactyloscopy haven't brought any applicable algorithm. For the time being, one has to settle for fingerprints only as means of authentication, not as source of passwords for decrypting one's enciphered content.
Additional reading:
Overview of current technology: http://sourceforge.net/apps/mediawiki/sourceafis/ (section Similar projects)
Launchpad discussion on a related matter: bug #276384
Handbook of Fingerprint Recognition: http://bias.csr.unibo.it/maltoni/handbook/

Note on libpam-fprint
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The PAM module contained in libpam-fprint has been obsoleted by libpam-fprintd (note the final “d”). Although the latest version of libpam-fprint is available from this PPA, its use is discouraged as it has several shortcomings compared to its successor, libpam-fprintd. If, for whatever reason, you decide to install libpam-fprint, make sure you read /usr/share/doc/libpam-fprint/README.Debian for caveats.